Processes for etching synthetic polymer resins with alkaline alkali metal manganate solutions

ABSTRACT

Processes for etching synthetic polymer resins, particularly ABS resins, with aqueous, alkaline solutions of alkali metal manganate (VI) at low temperatures.

United States Patent Guisti [54] PROCESSES FOR ETCHING SYNTHETIC POLYMERRESINS WITH ALKALINE ALKALI METAL MANGANATE SOLUTIONS Medie B. Gulsti,Spring Valley, Ill.

Cal-us Corporation, La Salle, 11].

May 13, 1970 [72] Inventor:

Assignee:

Filed:

Appl. No.:

[56] References Cited UNITED STATES PATENTS 2,939,772 6/1960 Newman etal ..2 52/79.5

[451 Mar. 28, 1972 3,425,947 2/1969 Rausch et al. ..252/79.5 3,489,625l/l970 Dell et a1. .,252/79.5

OTHER PUBLICATIONS Zahn et al., Electroplating ABS Graft Polymers,"56(11) 773- 779 1966) of Kunstoffe.

Primary Examiner-Robert F. Burnett Assistant Examiner-R. J. RocheAttorney-Johnston, Root, O'Keeffe, Keil, Thompson & Shurtleff ABSTRACTProcesses for etching synthetic polymer resins, particularly ABS resins,with aqueous, alkaline solutions of alkali metal manganate (VI) at lowtemperatures.

3 Claims, No Drawings INTRODUCTION Synthetic polymer resins, such asacrylonitrile-butadienestyrene interpolymers (ABS plastics), can beprepared for electroless plating with acidic oxidizing systems. Thesesystems have usually consisted of an oxidizing agent, such as chromicacid and a strong acid, such as sulfuric acid. The toxicity of thechromium compounds, their potential hazards as water pollutants, and thefairly high temperatures (55-70 C.) at which these systems are operatedhave been some of the disadvantages associated with these systems. Asystem which would produce similar etching of plastic articles made fromthe synthetic polymer resins but which has fewer of these disadvantageshas long been sought.

THE INVENTION It is a principal object of this invention to provide aunique kind of etching pretreatment of plastic objects, particularlythose made of electroplatable grades of ABS resins, which are to befirst electrolessly and then electrolytically plated.

It is another object of this invention to provide an etching processwith a chromium-free, manganate (VI) etching bath at temperaturesbetween 25 and 550 C.

This invention concerns chromium-free etching of synthetic polymerresins, particularly acrylonitrile-butadiene-styrene interpolymers (ABSplastics), at temperatures between about 25 and 555 C. The etchingcompositions consist essentially of 2.5 to 8.5 percent potassium and/orsodium manganate (Vl), 30 to 70 percent sodium and/or potassiumhydroxide, and 2l.567.5 percent water.

The most favorable concentration ranges for these compositions are 40-70g./l. (4-7%) of the alkali metalmanganate (Vl), 400-600 g./l. (40-60%)of the alkali metal hydroxide, and 230-560 g./l. (23-56%) water,although compositions with concentrations as low as 30 g./l. alkalimetal manganate, 300 g./l. alkali metal hydroxide, and 670 g./l. watermay demonstrate some etching ability. Temperature ranges for the use ofthese etching baths are from 25 to 55 C. in general, as the manganateion concentration increases, the temperature required for etching islower, and that as both temperature and manganate concentration areincreased, the time required for sufficient etching decreases. A five tothirty minute etching period generally is used.

The object of electrolessly depositing a layer of adherent metal on theplastic surface is to provide a base for electrolytic metal plating.Once the electroless deposit is laid, then plating can proceed in muchthe same way as if a metal were being electroplated.

The usual four steps in electroless plating are conditioning,

sensitizing, activating and chemical plating.

Conditioning prepares the surface to accept and hold a metal deposit. Itis sometimes called roughening, and may be accomplished physically(abrasion) or chemically (etching). Usually etching is achieved bysoaking in an acidic-oxidizing solution, such as the H SO -CrO etch.

Sensitizing and activating are two steps which accomplish the following:deposit of a thin layer of a tin (II) salt, usually stannous chloride,followed by a dip into a solution containing a noble metal (platinum orpalladium salt). The tin is oxidized, and the platinum or palladium isreduced to the metal. The concentration of stannous chloride in thesensitizer is usually about g./l., and the concentration of palladiumchloride in the activator is usually between 0.25 and 0.5 g./l. Thereare various ways to accomplish this end, and different methods and namesare used for these two steps, and sometimes they are combined in onestep. However, the end result is a fine film of a noble metal whichserves as a catalyst for the electroless metal deposition in the finalstep.

Plating is the final step of the electroless plating procedure. Bothcopper and nickel have been used. Sometimes a layer of copper is firstdeposited, followed by a layer of nickel. Copper systems usually consistof copper salts, caustic, other salts, and formaldehyde. Nickel systemsusually contain nickel salts and strong reducing agents, such as boranesor hypophosphites.

Water rinses are used between each step to avoid contamination of thebaths.

The invention will be further appreciated from the following examples.

EXAMPLE 1 Potassium manganate (V1) is produced in situ by the reactionof potassium permanganate and an alkali metal hydroxide at a temperatureof -90 C. Fifty grams of KOH, 5 g. of KMnO and 20 g. of water are mixedand heated to 80-90 C with stirring. The mixture is held at thistemperature with stirring until deoxidation reaction is complete, andthe solution is bright green. Twenty grams of water are added and thesolution is allowed to cool to working temperature. At 40 C., a piece ofABS plastic is etched in this solution for 10 minutes. Satisfactoryadhesion of the electroless nickel deposit is achieved.

Adhesion characteristics are judged by several criteria. First a pieceof scotch tape was pressed on the freshly electrolessplated plastic andthereafter removed. The tape was then checked to see if any of the metaldeposit was pulled off by the pressure sensitive adhesive 'Second, theappearance of the plating is observed to ascertain whether it had asmooth, evenly distributed, glossy finish. Third, the plated plastic wasobserved under a microscope to check for a fine, smooth grain, eventexture and good coverage of the plastic surface by theelectroless-plated metal. Fourth, a piece of freshly electroless-platedplastic is scratched in such a way that the plastic substrate formed acurl. The adhesion on the metal deposition to this curl is inspectedunder the microscope. Finally, by a simple scratch test involvingscratching of the electrolessplated metal with a fingernail, adhesion isevaluated as being good if the surface is difiicult or impossible toscratch.

EXAMPLE 2 Forty-five grams of NaOH, 6 gm. of NaMnO and 20 gms. of waterare mixed and heated to 8090 C., with stirring, to produce sodiummanganate (VI). Twenty-nine grams of water are added, and the solutionused as an etchant for ABS plastic at a temperature of 30 C. for 20minutes. Satisfactory etching is achieved EXAMPLE 3 Twenty-five gramsNaOl-l 25 g. of KOH, 2.5 g. of KMnO,, 2.5 g. of NaMnO,, and 20 g. ofwater are stirred and heated to 8090 C., to produce a mixed manganate(VI) solution. Twenty grams of water are added, and the solution used asan etchant for ABS plastic at a temperature of 30 C. for 20 minutes.Satisfactory etching is achieved.

The aforesaid ABS plastics may be reinforced with fiberglass.Preferably, they are graft polymers or polymer blends of the typedescribed in Us. Pat. No. 3,445,350. The blends contain at least 20percent by weight of ABS graft polymer, the remainder being polyvinylchloride, polyurethane, polycarbonates, etc.

It is thought that the invention and its numerous attendant advantageswill be fully understood from the foregoing description, and it isobvious that numerous changes may be made in the form, construction andarrangement of the several parts without departing from the spirit orscope of the invention, or sacrificing any of its attendant advantages,the forms herein disclosed being preferred embodiments for the purposeof illustrating the invention.

The invention is hereby claimed as follows:

1. A process for pretreatment of an electroplatable synthetic polymerarticle containing at least 20 percent of anacrylonitrile-butadiene-styrene interpolymer to be electrolessly platedwhich comprises etching a synthetic polymer surface 3. A process'asclaimed in claim 1 wherein said polymer article is made of anelectroplatable acrylonitrile-butadienestyrene graft polymer, andwherein said etching solution consists essentially of 4-7 percentpotassium manganate (Vl), sodium manganate (Vl), or mixtures thereof,40-60 percent potassium hydroxide, sodium hydroxide, or mixturesthereof, and 23-56 percent water, said percentages being by weight.

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2. A process as claimed in claim 1 wherein said polymer article is madeof an electroplatable acrylonitrile-butadiene-styrene graft polymer. 3.A process as claimed in claim 1 wherein said polymer article is made ofan electroplatable acrylonitrile-butadiene-styrene graft polymer, andwherein said etching solution consists essentially of 4-7 percentpotassium manganate (VI), sodium manganate (VI), or mixtures thereof,40-60 percent potassium hydroxide, sodium hydroxide, or mixturesthereof, and 23-56 percent water, said percentages being by weight.